Synthesis and characterization of metakaolin-based geopolymer systems under cyclic thermal exposure

Abstract

Geopolymers are low-carbon binders that have garnered significant interest in the construction industry due to their potential in applications where Portland cement may not be the optimal choice, particularly in environments exposed to repeated high temperatures. While most existing studies have focused on single-heat exposure scenarios, predominantly assessing the behavior of geopolymers under fire-like conditions, a more comprehensive evaluation of their resistance to high temperatures and refractoriness requires testing under multiple heating cycles. Such testing is crucial to determine whether these materials can withstand repeated thermal stresses over time. In this context, the present study investigates the performance of metakaolin-based geopolymers subjected to 10 thermal cycles at 400, 600, 800, and 1000 °C. The formulations tested included varying alkali dosages (15% and 20% K₂O) and SiO₂/K₂O silica modulus (Ms) of the alkaline solution ranging from 1.0 to 1.25. The results revealed a decrease in density and an increase in water absorption following thermal exposure. Although a significant strength loss was observed after the first cycle, the geopolymers demonstrated remarkable thermal stability between the first and tenth cycles. Depending on the formulation, the study suggests that geopolymers exhibit considerable resilience to high-temperature conditions, with water content playing a crucial role in the material’s thermal response and overall performance.